RegistryKey reg = Registry.LocalMachine.
OpenSubKey(@"Software\Microsoft\Windows\CurrentVersion\Run", true);
// set value of "abc" to "efd"
reg.SetValue("abc", "efd", RegistryValueKind.DWord);
// get value of "abc"; return 0 if value not found
string value = (string)reg.GetValue("abc", "0");